She's not out of line to "question" or voice her views to the Captain on the situation. If this is reported accurately though, she was out-of-line for trying to overrule him, and especially to try do so publicly in front of passengers, once the decision was made by the Captain, who even under current CRM practices still has the primary authority and responsibility for the aircraft and its passengers, especially as the Captain's decision was a decision that was MORE CONSERVATIVE and MORE CAUTIOUS for safety. It's not like we're discussing a case where the Captain decided to try to takeoff in a thunderstorm with hail and 50 mph winds and severe windshear and the FA was voicing her objections to that.

Put another way, if I'm on an email with a client and someone higher up than me, and the higher-up gives bad advice, I go talk to that higher-up (or in extreme circumstances/ with approval of that higher-up - their boss). In no circumstances would it be appropriate for me to email the client and tell them that what my higher-up said was wrong.

This is an excellent comparison, IMO.

If the FA disagreed that strongly, she could have easily caught up with the captain and quietly said "If you're deplaning because of the heat, it's actually starting to feel much cooler in the back" or whatever was on her mind.

If she's relaying something to a passenger, a simple, "I'm going to go check with the captain on that" would suffice. There's no need to announce to your customers that you're in complete disagreement and are about to attempt to reverse a decision. In fact, if the roles were reversed, I'd expect exactly the same of the captain, too - pull the FA aside, figure it out quietly, and don't announce to pax that you think your lead FA is wrong.

You left out a "U" between the "M" and the "O."

All crew members are entitled and indeed obligated to speak up, and the captain has an obligation to create an environment where they feel comfortable doing so--that's just basic CRM.

They can't "overrule" them, though--the final decision rests with the person in charge.

But that's not what happened here. So many keep trying to point to non-sequiturs or examples of CRM or lack thereof that they think apply and actually don't in this situation, only demonstrating further how many on this forum don't know what CRM is and how it actually works in various situations. In your example, what you have is a case of a Captain needing a "Go" from everyone (the GA, dispatch, all flight crew, etc.) prior to departing. The FA voicing an objection due to smelling alcohol is not giving the "Go" for departure so the plane is going nowhere (unless the pilot truly takes actions into his own hands, in which case the Captain would have more problems than just the alcohol on his breath and yes, the FA should take further action to get proper authorities or prevent the aircraft from departing). In this case that is the subject of the thread, the FA was thinking she had the opposite power - that she could allow passengers to board or allow them to stay onboard despite not having an okay from all required personnel who must give the okay to have passengers on the plane. The Captain made a decision. His "no-go" was enough for people to get off, especially because the aircraft was parked at the gate, with a jetway attached to the plane. It's not like passengers were going slides here. And given that it was one that resulted in no danger - as I've previously mentioned, it was a more conservative decision with regards to safety. If Ops thinks the decision was wrong, then they can work that with pilot. But at this point, it wasn't the FA's call. It was the Captain's. Whether the FA thought it was wrong or not should have stayed between her and the Captain and been discussed between her and the Captain in private or with the appropriate department within DL's organization, not to the passengers.

I don't always agree with the decisions of my chain-of-command but unless it's an illegal order, I'm expected to follow those orders. It would be completely unprofessional of me to say "I don't agree with this - don't do it" to others in my organization or even just say "I don't agree with this" to other members of my organization. This undermines leadership and also undermines the relationship between me and my leadership and only results in more harm than good, both short term and long term. In this case here, the FA, despite not agreeing with the Captain's decision, should have come on the jet and simply said "Ladies and gentleman, the Captain has ordered everyone off the plane for XXXX reason. Please collect your belongings and deplane. More information will be provided when it becomes available and DL agents will be available to assist you with rebooking options if you require".

Another day, another FT Rorschach Test thread...

And you would want the subordinate to do that openly/vocally in front of your customers, even when the subordinate may not know all the facts of the situation, and when your customers almost certainly do not know all the facts of the situation?

If your answer is "yes", then I guess you and I just have fundamentally different approaches to business operations and customer engagement.

I literally just got off the phone with a couple people who were in disagreement about how to proceed with a customer. The manager made a decision during a meeting, their team member thought it was a bad idea, they talked about it privately, and then they escalated it to me to figure out. We came to an agreement on what to do and they both went back to the customer aligned on their talking points. Customer has no idea there was internal disagreement and for all they know we simply came into new information that resulted in us adjusting our approach. IMO, that's how you're supposed to handle internal disagreements. Obviously in the situation OP described, this could be done in a matter of seconds or minutes vs. the series of phone calls across different locations/timezones I was engaged in for the past 45 minutes, but the same principles apply.

How do you know that that's what was going on in this particular case, though?

Not necessarily, as I explained above. Things that aren't an emergency situation on the ground can become one in the air; in that case, the plane's not going anywhere anytime soon, so you deplane.

Why are you so reluctant to acknowledge that you don't have all the information here, certainly less than the actual professionals charged with making these decisions? How arrogant can you be?

I don't think anyone is really disagreeing with this. And in my scenario above, if I knew what my higher-up said to the client was wrong, and I didn't go talk to him/her about it, I wouldn't be doing my job. When anyone, even the leader of our practice group, tells a client something that's incorrect, he would not only want, he would demand that someone calls him out on it. But the appropriate means to call him out on it is not by correcting the statement directly to the client. It's that simple.